U.S. patent number 7,923,479 [Application Number 12/185,462] was granted by the patent office on 2011-04-12 for superabsorbent foam, method for the production thereof, and use thereof.
This patent grant is currently assigned to BASF Aktiengesellschaft. Invention is credited to Samantha Champ, Andreas Reifschneider, Mariola Wanior.
United States Patent |
7,923,479 |
Champ , et al. |
April 12, 2011 |
Superabsorbent foam, method for the production thereof, and use
thereof
Abstract
Superabsorbent foam comprising superabsorbent fiber and/or fruit
fiber, processes for producing superabsorbent foam having improved
wet strength by foaming a crosslinkable aqueous mixture comprising
at least 50 mol % neutralized acid-functional monoethylenically
unsaturated monomer or at least one basic polymer, crosslinker,
superabsorbent synthetic fiber and/or fruit fiber and at least one
surfactant and subsequently polymerizing the monomer in the foamed
mixture or crosslinking the basic polymer to form a hydrogel foam
and use of the thus obtainable foam in hygiene articles to absorb
body fluids, in dressing material to cover wounds, as a sealing
material, as a packaging material, as a soil improver, as a soil
substitute, to dewater sludges, to thicken waterborne paints or
coatings in the course of disposing of residual quantities thereof,
to dewater water-containing oils or hydrocarbons or as a material
for filters in ventilation systems.
Inventors: |
Champ; Samantha (Ludwigshafen,
DE), Wanior; Mariola (Erlensee, DE),
Reifschneider; Andreas (Mannheim, DE) |
Assignee: |
BASF Aktiengesellschaft
(Ludwigshafen, DE)
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Family
ID: |
32038445 |
Appl.
No.: |
12/185,462 |
Filed: |
August 4, 2008 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20090045138 A1 |
Feb 19, 2009 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10530373 |
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PCT/EP03/11013 |
Oct 6, 2003 |
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Foreign Application Priority Data
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Oct 10, 2002 [DE] |
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102 47 241 |
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Current U.S.
Class: |
521/99 |
Current CPC
Class: |
C08J
9/0085 (20130101); A61L 15/60 (20130101); C09K
3/1028 (20130101); A61L 15/425 (20130101); B01J
20/26 (20130101); C08J 9/28 (20130101); C08J
2207/12 (20130101); C08J 2300/14 (20130101) |
Current International
Class: |
C08G
18/48 (20060101); C08J 9/00 (20060101) |
Field of
Search: |
;521/50,64,79,99 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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102 04 980.7 |
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Feb 2002 |
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DE |
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0 264 208 |
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Apr 1988 |
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EP |
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0 436 514 |
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Jul 1991 |
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EP |
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693525 |
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Jan 1996 |
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EP |
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0 858 478 |
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Aug 1998 |
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EP |
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WO-97/31600 |
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Sep 1997 |
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WO |
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WO-97/31971 |
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Sep 1997 |
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WO |
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WO-99/44648 |
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Sep 1999 |
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WO |
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WO-00/52087 |
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Sep 2000 |
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WO |
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Other References
Machine Translation of EP0693525. cited by examiner.
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Primary Examiner: Eashoo; Mark
Assistant Examiner: Scott; Angela C
Attorney, Agent or Firm: Marshall, Gerstein & Borun
LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This is a continuation of U.S. patent application Ser. No.
10/530,373, filed Apr. 6, 2005, pending, which claims the benefit
of International Application No. PCT/EP2003/011013, filed Oct. 6,
2003, which claims the benefit of German patent application No. 102
47 241.6, filed Oct. 10, 2002.
Claims
We claim:
1. A superabsorbent foam comprising from 0.1 to 5% by weight of a
natural fiber selected from the group consisting of apple fiber,
orange fiber, tomato fiber, wheat fiber, oat fiber, and mixtures
thereof; said superabsorbent foam obtainable by foaming a
polymerizable aqueous mixture comprising at least 50 mol%
neutralized acid-functional monoethylenically unsaturated monomer
or at least one basic polymer, a crosslinker, the natural fiber,
and at least one surfactant, and subsequently polymerizing and/or
crosslinking the foamed mixture.
2. The superabsorbent foam of claim 1 wherein the foam is surface
postcrosslinked.
3. The superabsorbent foam of claim 1 wherein the polymerizable
aqueous mixture comprises at least a 50% aqueous sodium or
potassium hydroxide solution neutralized acrylic acid, a
crosslinker containing at least two ethylenically unsaturated
double bonds, a radical-forming initiator, the natural fiber, and
at least one surfactant.
4. The superabsorbent foam of claim 1 wherein the polymerizable
aqueous mixture comprises at least one basic polymer selected from
the group consisting of polymers containing vinylamine units,
polymers containing vinylguanidine units, polymers containing
dialkylaminoalkyl(meth)acrylamide units, polyethyleneimines,
ethyleneimine-grafted polyamidoamines, and
polydiallyldimethylammonium chlorides.
5. An article comprising the superabsorbent foam of claim 1.
6. The article of claim 5 selected from the group consisting of a
hygiene article to absorb body fluids, a dressing article to cover
wounds, and a ventilation system filter.
7. A method of dewatering a liquid comprising contacting the liquid
with a superabsorbent foam of claim 1.
8. The method of claim 7 wherein the liquid is a sludge or a
water-containing oil or hydrocarbon.
9. A sealing or packaging material comprising a superabsorbent foam
of claim 1.
10. A soil adjuvant comprising a superabsorbent foam of claim
1.
11. A method of thickening an aqueous liquid to facilitate disposal
thereof, comprising admixing the aqueous liquid with a
superabsorbent foam of claim 1 to thicken the aqueous liquid.
12. A superabsorbent foam comprising at least one natural fiber
selected from the group consisting of apple fiber, orange fiber,
tomato fiber, wheat fiber, oat fiber, and mixtures thereof; said
superabsorbent foam obtainable by foaming a polymerizable aqueous
mixture comprising at least a 50 mol% neutralized acid-functional
monoethylenically unsaturated monomer or at least one basic
polymer, a crosslinker, the natural fiber, and at least one
surfactant, and subsequently polymerizing and/or crosslinking the
foamed mixture, wherein the polymerizable aqueous mixture contains
from 0.05 to 5% by weight of natural fiber, based on the
monomer.
13. The superabsorbent foam of claim 12 further comprising from 1%
to 60% water, by weight of the superabsorbent foam.
14. A process for producing a superabsorbent foam having improved
wet strength, which comprises foaming a crosslinkable aqueous
mixture comprising at least a 50 mol% neutralized acid-functional
monoethylenically unsaturated monomer or at least one basic
polymer, a crosslinker, a natural fiber selected from the group
consisting of apple fiber, orange fiber, tomato fiber, wheat fiber,
and mixtures thereof, and at least one surfactant, and subsequently
polymerizing the monomer in the foamed mixture or crosslinking the
basic polymer in the foamed mixture to form a hydrogel foam,
wherein the aqueous mixture comprises from 0.1 to 5% by weight of
the natural fiber.
15. The process of claim 14 wherein the foaming of the aqueous
polymerizable mixture is effected by dissolving an inert gas in the
mixture at from 2 to 400 bar and subsequently decompressing the
mixture to atmospheric.
Description
DESCRIPTION
This invention relates to superabsorbent foam obtainable by foaming
a polymerizable aqueous mixture and polymerizing the foamed
mixture, a process for producing superabsorbent foam and the use of
the foam in hygiene articles to absorb body fluids.
Water-absorbent, predominently open-cell foams based on crosslinked
acid-functional monomers are known, cf EP-B-0 858 478,
WO-A-99/44648 and WO-A-00/52087. They are produced for example by
foaming a polymerizable aqueous mixture which comprises at least 50
mol % neutralized acid-functional monoethylenically unsaturated
monomer, crosslinker and at least one surfactant and subsequently
polymerizing the foamed mixture. The foaming of the polymerizable
mixture may be effected for example by dispersing fine bubbles or a
radical-inert gas or by dissolving such a gas under elevated
pressure in the polymerizable mixture and decompressing the
mixture. The water content of the foams is adjusted to 1-60% by
weight for example. The foams may optionally be subjected to
surface postcrosslinking by spraying a crosslinker onto the foamed
material or immersing the foam therein and heating the
crosslinker-laden foam to a higher temperature. The foams are used
for example in hygiene articles to acquire, distribute and store
body fluids.
WO-A-97/31600 discloses an absorber element for use in hygiene or
sanitary articles which has a plurality of elements composed of a
superabsorbent foam arranged on a support in a grid pattern at
distances so that the elements in the swollen state touch at their
peripheries. It is possible for example for a monomer foam to be
applied to the support in the desired grid pattern and subsequently
polymerized on the support or for separately produced foam elements
to be chemically or physically fixed on the support in the desired
grid pattern. However, the wet strength of the above-described
superabsorbent foams is in need of improvement.
Known superabsorbent fiber is obtainable for example by
neutralizing the carboxyl groups of a hydrolyzed copolymer of
isobutene and maleic anhydride with aqueous sodium hydroxide
solution to 20-80%, adding a bifunctional compound capable of
reacting with the nonneutralized carboxyl groups of copolymer, eg
propylene glycol or ethanolamine, and then substantially removing
the water from the solution to leave the solution with a solids
content of 45%. This solution is subsequently spun into fiber. The
fiber is thereafter heated to a comparatively high temperature, for
example 210.degree. C., to crosslink the copolymer. The crosslinked
copolymer has superabsorbent properties. It is used for example in
baby diapers, tampons, sanitary napkins, surgical sponges and
dressings to absorb body fluids. Such superabsorbent fiber is
known, cf for example EP-B-0 264 208, EP-B-0 272 072, EP-B-0 436
514 and U.S. Pat. No. 4,813,945.
Prior DE application 102 04 980.7, unpublished at the priority date
of the present invention, discloses foams of water-absorbing basic
polymer which are obtainable by foaming an aqueous mixture
comprising at least one basic polymer such as polyvinylamine and at
least one crosslinker such as glycidyl ether and then crosslinking
the foamed mixture. The wet strength of the water-absorbing foams
thus obtainable is likewise in need of improvement.
It is an object of the present invention to improve the wet
strength of the water-absorbing foam.
We have found that this object is achieved according to the
invention by superabsorbent foam comprising superabsorbent
synthetic fiber and/or natural fiber selected from the group
consisting of apple fiber, orange fiber, tomato fiber, wheat fiber
and/or oat fiber. Such foam is obtainable by foaming a
polymerizable aqueous mixture comprising at least 50 mol %
neutralized acid-functional monoethylenically unsaturated monomer
or at least one basic polymer, crosslinker, superabsorbent fiber
and at least one surfactant and subsequently polymerizing and/or
crosslinking the foamed mixture.
The present invention also provides a process for producing
superabsorbent foam having improved wet strength, which comprises
foaming a crosslinkable aqueous mixture comprising at least 50 mol
% neutralized acid-functional monoethylenically unsaturated monomer
or at least one basic polymer, crosslinker, superabsorbent
synthetic fiber and/or natural fiber selected from the group
consisting of apple fiber, orange fiber, tomato fiber, wheat fiber
and/or oat fiber and at least one surfactant and subsequently
polymerizing the monomer in the foamed mixture or crosslinking the
basic polymer to form a hydrogel foam.
Foams based on crosslinked acid-functional addition polymers are
known from the cited prior art references EP-B-0 858 478 page 2
line 55 to page 18 line 22, WO-A-99/44648 and WO-A-00/52087 page 5
line 23 to page 41 line 18. The known processes comprise initially
foaming an aqueous mixture which comprises for example a) from 10
to 80% by weight of acid-functional monoethylenically unsaturated
monomer which is at least 50 mol % neutralized, b) optionally up to
50% by weight of other monoethylenically unsaturated monomer, c)
from 0.001 to 5% by weight of crosslinker, d) initiators, e) from
0.1 to 20% by weight of at least one surfactant, f) optionally a
solubilizer, and g) optionally thickeners, foam stabilizers,
polymerization regulators, fillers and/or cell nucleators.
However, it is also possible to foam an aqueous mixture which,
instead of said monomers (a) and (b), contains a basic polymer
whose basic groups have optionally been partly neutralized. The
aqueous mixtures can be foamed for example by dispersing fine
bubbles of radical-inert gas in the mixture or dissolving such a
gas in the crosslinkable mixture at from 2 to 400 bar and
subsequently decompressing the mixture to atmospheric. This
provides a flowable foam which can be filled into molds or cured on
a belt. Curing is effected by addition polymerization when
acid-functional monomers, optionally other monoethylenically
unsaturated monomers and crosslinkers are used and by crosslinking
when basic polymers are used.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1 and 2 are schematic diagrams of an instrument for measuring
a Wet Failure Value (WFV) of a superabsorbent foam; and
FIG. 3 is a side view of a metal plate used in the instrument for
measuring the WFV of a superabsorbent foam.
BASIC POLYMERS
Useful basic polymers include for example polymers containing
vinylamine units, polymers containing vinylguanidine units,
polymers containing dialkylaminoalkyl(meth)acrylamide units,
polyethyleneimines, ethyleneimine-grafted polyamidoamines and
polydiallyldimethylammonium chlorides.
Polymers containing vinylamine units are known, of U.S. Pat. No.
4,421,602, U.S. Pat. No. 5,334,287, EP-A-0 216 387, U.S. Pat. No.
5,981,689, WO-A-00/63295 and U.S. Pat. No. 6,121,409. They are
prepared by hydrolysis of polymers containing open-chain
N-vinylcarboxamide units. These polymers are obtainable for example
by polymerizing N-vinylformamide, N-vinyl-N-methylformamide,
N-vinylacetamide, N-vinyl-N-methylacetamide,
N-vinyl-N-ethylacetamide and N-vinylpropionamide. The monomers
mentioned can be polymerized either alone or together with other
monomers.
Useful monoethylenically unsaturated monomers for copolymerization
with the N-vinylcarboxamides include all compounds copolymerizable
therewith. Examples thereof are vinyl esters of saturated
carboxylic acids of 1 to 6 carbon atoms such as vinyl formate,
vinyl acetate, vinyl propionate and vinyl butyrate and vinyl ethers
such as C.sub.1-C.sub.6-alkyl vinyl ethers, for example methyl
vinyl ether or ethyl vinyl ether. Useful comonomers further include
esters, amides and nitriles of ethylenically unsaturated
C.sub.3-C.sub.6-carboxylic acids, for example methyl acrylate,
methyl methacrylate, ethyl acrylate and ethyl methacrylate,
acrylamide and methacrylamide and also acrylonitrile and
methacrylonitrile.
Useful carboxylic esters are further derived from glycols or
polyalkylene glycols, in either case only one OH group being
esterified, for example hydroxyethyl acrylate, hydroxyethyl
methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate,
hydroxypropyl methacrylate, hydroxybutyl methacrylate and also
acrylic monoesters of polyalkylene glycols having a molar mass from
500 to 10 000. Useful comonomers further include esters of
ethylenically unsaturated carboxylic acids with amino alcohols such
as for example dimethylaminoethyl acrylate, dimethylaminoethyl
methacrylate, diethylaminoethyl acrylate, diethylaminoethyl
methacrylate, dimethylaminopropyl acrylate, dimethylaminopropyl
methacrylate, diethylaminopropyl acrylate, dimethylaminobutyl
acrylate and diethylaminobutyl acrylate. The basic acrylates can be
used in the form of the free bases, in the form of their salts with
mineral acids such as hydrochloric acid, sulfuric acid or nitric
acid, in the form of their salts with organic acids such as formic
acid, acetic acid, propionic acid or sulfonic acids or in
quaternized form. Useful quaternizing agents include for example
dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride
or benzyl chloride.
Useful comonomers further include amides of ethylenically
unsaturated carboxylic acids such as acrylamide, methacrylamide and
also N-alkylmonoamides and -diamides of monoethylenically
unsaturated carboxylic acids having alkyl moieties of 1 to 6 carbon
atoms, for example N-methylacrylamide, N,N-dimethylacrylamide,
N-methylmethacrylamide, N-ethylacrylamide, N-propylacrylamide and
tert-butylacrylamide and also basic (meth)acrylamides, for example
dimethylaminoethylacrylamide, dimethylaminoethylmethacrylamide,
diethylaminoethylacrylamide, diethylaminoethylmethacrylamide,
dimethylaminopropylacrylamide, diethylaminopropylacrylamide,
dimethylaminopropylmethacrylamide and
diethylaminopropylmethacrylamide.
Useful comonomers further include N-vinylpyrrolidone,
N-vinylcaprolactam, acrylonitrile, methacrylonitrile,
N-vinylimidazole and also substituted N-vinylimidazoles such as for
example N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole,
N-vinyl-5-methylimidazole, N-vinyl-2-ethylimidazole and
N-vinylimidazolines such as N-vinylimidazoline,
N-vinyl-2-methylimidazoline and N-vinyl-2-ethylimidazoline.
N-Vinylimidazoles and N-vinylimidazolines are used not only in the
form of the free bases but also after neutralization with mineral
acids or organic acids or in quaternized form, in which case the
quaternization is preferably effected using dimethyl sulfate,
diethyl sulfate, methyl chloride or benzyl chloride. It is further
possible to use diallyldialkylammonium halides, for example
diallyldimethylammonium chloride.
The copolymers contain for example from 95 to 5 mol % and
preferably from 90 to 10 mol % of at least one N-vinylcarboxamide,
and from 5 to 95 mol %, and preferably from 10 to 90 mol % of other
monoethylenically unsaturated monomers copolymerizable therewith in
copolymerized form. The comonomers are preferably free of acid
groups.
To prepare polymers containing vinylamine units, it is preferable
to start from homopolymers of N-vinylformamide or from copolymers
obtainable by copolymerizing N-vinylformamide with vinyl formate,
vinyl acetate, vinyl propionate, acrylonitrile, N-vinylcaprolactam,
N-vinylurea, N-vinylpyrrolidone or C.sub.1-C.sub.6-alkyl vinyl
ethers and subsequently hydrolyzing the homo- or copolymers to form
vinylamine units from the copolymerized N-vinylformamide units, the
degree of hydrolysis being for example in the range from 5 to 100
mol % and preferably in the range from 70 to 100 mol %. The
hydrolysis of the above-described polymers is effected according to
known processes by the action of acids, bases or enzymes. When
acids are used as a hydrolyzing agent, the vinylamine units of the
polymers are present as an ammonium salt, whereas the hydrolysis
with bases gives rise to free amino groups.
The degree of hydrolysis of the homopolymers of the
N-vinylcarboxamides and their copolymers can be in the range from 5
to 100 mol % and is preferably in the range from 70 to 100 mol %.
In most cases, the degree of hydrolysis of the homo- and copolymers
is in the range from 80 to 95 mol %. The degree of hydrolysis of
the homopolymers is equivalent to the level of vinylamine units in
the polymers. In the case of copolymers which contain vinyl esters
in copolymerized form, the hydrolysis of the N-vinylformamide units
may be accompanied by a hydrolysis of the ester groups to form
vinyl alcohol units. This is particularly the case when the
hydrolysis of the copolymers is conducted in the presence of
aqueous sodium hydroxide solution. Polymerized units of
acrylonitrile will likewise undergo chemical changes in the course
of the hydrolysis, producing for example amide groups or carboxyl
groups. The homo- and copolymers containing vinylamine units may
contain up to 20 mol % of amidine units, for example due to a
reaction of formic acid with two adjacent amino groups or due to
intramolecular reaction of an amino group with an adjacent amide
group, for example of copolymerized N-vinylformamide. The molar
masses of the polymers containing vinylamine units range for
example from 500 to 10 million and preferably from 1000 to 5
million (determined by light scattering). This molar mass range
corresponds for example to K values from 5 to 300 and preferably
from 10 to 250 (determined after H. Fikentscher in 5% aqueous
sodium chloride solution at 25.degree. C. and at a polymer
concentration of 0.5% by weight).
The polymers containing vinylamine units are preferably used in
salt-free form. Salt-free aqueous solutions of polymers containing
vinylamine units are preparable for example from the
above-described salt-containing polymer solutions by
ultrafiltration using suitable membranes having molecular weight
cutoffs at for example from 1000 to 500 000 dalton and preferably
at from 10 000 to 300 000 dalton. Similarly, the hereinbelow
described aqueous solutions of other polymers containing amino
and/or ammonium groups can be obtained in salt-free form by
ultrafiltration.
Similarly, derivatives of polymers containing vinylamine units can
be used as polymers forming basic hydrogels. For instance, polymers
containing vinylamine units can be subjected to amidation,
alkylation, sulfonamide formation, urea formation, thiourea
formation, carbamate formation, acylation, carboxymethylation,
phosphonomethylation or Michael addition of the amino groups of the
polymer to prepare a multiplicity of suitable hydrogel derivatives.
Of particular interest here are uncrosslinked polyvinylguanidines
which are accessible by reaction of polymers containing vinylamine
units, preferably polyvinylamines, with cyanamide
(R.sup.1R.sup.2N--CN where R.sup.1, R.sup.2.dbd.H, C1-C4-alkyl,
C3-C6-cycloalkyl, phenyl, benzyl, alkyl-substituted phenyl or
naphthyl) cf U.S. Pat. No. 6,087,448 column 3 line 64 to column 5
line 14.
Polymers containing vinylamine units further include hydrolyzed
graft polymers of for example N-vinylformamide on polyalkylene
glycols, polyvinyl acetate, polyvinyl alcohol, polyvinylformamides,
polysaccharides such as starch, oligosaccharides or
monosaccharides. The graft polymers are obtainable for example by
free-radically polymerizing N-vinylformamide in an aqueous medium
in the presence of at least one of the grafting bases mentioned,
optionally together with copolymerizable other monomers, and
subsequently hydrolyzing the engrafted vinylformamide units in a
known manner to obtain vinylamine units.
Useful for the preparation of polymers water-absorbing basic
polymers further include polymers of
dialkylaminoalkyl(meth)acrylamides. Useful monomers for preparing
such polymers include for example dimethylaminoethylacrylamide,
dimethylaminoethylmethacrylamide, dimethylaminopropylacrylamide,
dimethylaminopropylmethacrylamide, diethylaminoethylacrylamide,
diethylaminoethylmethacrylamide and diethylaminopropylacrylamide.
These monomers may be used in the form of the free bases, as salts
with inorganic or organic acids or in quaternized form in the
polymerization. They may be free-radically polymerized to
homopolymers or together with other copolymerizable monomers to
copolymers. The polymers contain for example at least 30 mol % and
preferably at least 70 mol % of the basic monomers mentioned.
Water-absorbing basic polymers based on
poly(dimethylaminoalkylacrylamide)s are known from U.S. Pat. No.
5,962,578.
Useful basic polymers further include polyethyleneimines, which are
preparable for example by polymerization of ethyleneimine in
aqueous solution in the presence of acid-detaching compounds, acids
or Lewis acids as a catalyst. Polyethyleneimines have for example
molar masses of up to 2 million and preferably from 200 to 1 000
000. Particular preference is given to using polyethyleneimines
having molar masses from 500 to 750 000. The polyethyleneimines may
optionally be modified, for example alkoxylated, alkylated or
amidated. They may also be subjected to a Michael addition or a
Strecker synthesis. The polyethyleneimine derivatives obtainable
thereby are likewise useful as basic polymers for preparing
water-absorbing basic polymers.
Useful basic polymers further include ethyleneimine-grafted
polyamidoamines, which are obtainable for example by condensing
dicarboxylic acids with polyamines and subsequently grafting with
ethyleneimine. Useful polyamidoamines are obtained for example by
reacting dicarboxylic acids having 4 to 10 carbon atoms with
polyalkylenepolyamines containing 3 to 10 basic nitrogen atoms in
the molecule. Examples of dicarboxylic acids are succinic acid,
maleic acid, adipic acid, glutaric acid, suberic acid, sebacic acid
and terephthalic acid. Polyamidoamines may also be prepared using
mixtures of dicarboxylic acids and likewise using mixtures of a
plurality of polyalkylenepolyamines. Useful polyalkylenepolyamines
include for example diethylenetriamine, triethylenetetramine,
tetraethylenepentamine, dipropylenetriamine, tripropylenetetramine,
dihexamethylenetriamine, aminopropylethylenediamine and
bisaminopropylethylenediamine. To prepare polyamidoamines, the
dicarboxylic acids and polyalkylenepolyamines are heated to
comparatively high temperatures, for example to temperatures in the
range from 120 to 220.degree. C. and preferably in the range from
130 to 180.degree. C. The water formed in the course of the
condensation is removed from the system. The condensation may
optionally also utilize lactones or lactams of carboxylic acids
having 4 to 8 carbon atoms. The amount of polyalkylenepolyamine
used per mole of a dicarboxylic acid is for example in the range
from 0.8 to 1.4 mol. These polyamidoamines are grafted with
ethyleneimine. The grafting reaction is carried out for example in
the presence of acids or Lewis acids such as sulfuric acid or boron
trifluoride etherates at for example from 80 to 100.degree. C.
Compounds of this kind are described in DE-B-24 34 816 for
example.
Useful basic polymers further include the optionally crosslinked
polyamidoamines, which may optionally additionally have been
grafted with ethyleneimine prior to any crosslinking. The
crosslinked ethyleneimine-grafted polyamidoamines are water soluble
and have for example an average molecular weight from 3000 to 2
million dalton. Customary crosslinkers include for example
epichlorohydrin or bischlorohydrin ethers of alkylene glycols and
polyalkylene glycols.
Useful basic polymers further include polyallylamines. Polymers of
this kind are obtained by homopolymerizing of allylamine,
preferably in acid-neutralized form, or by copolymerizing
allylamine with other monoethylenically unsaturated monomers
described above as comonomers for N-vinylcarboxamides.
Useful basic polymers further include water-soluble crosslinked
polyethyleneimines which are obtainable by reaction of
polyethyleneimines with crosslinkers such as epichlorohydrin or
bischlorohydrin ethers of polyalkylene glycols having from 2 to 100
ethylene oxide and/or propylene oxide units and which still have
free primary and/or secondary amino groups. Also suitable are
amidic polyethyleneimines which are obtainable for example by
amidation of polyethyleneimines with
C.sub.1-C.sub.22-monocarboxylic acids.
Useful cationic polymers further include alkylated
polyethyleneimines and alkoxylated polyethyleneimines. The
polyethyleneimine is alkoxylated using for example from 1 to 5
ethylene oxide or propylene oxide units per NH unit in the
polyethyleneimine.
The abovementioned basic polymers have for example K values from 8
to 300 and preferably from 15 to 180 (determined after H.
Fikentscher in 5% aqueous sodium chloride solution at 25.degree. C.
and a polymer concentration of 0.5% by weight). At pH 4.5 their
charge density is for example not less than 1 and preferably not
less than 4 meq/g of polyelectrolyte.
Preferred basic polymers include polymers containing vinylamine
units, polyvinylguanidines and polyethyleneimines. Examples thereof
are:
vinylamine homopolymers, 10-100% hydrolyzed polyvinylformamides,
partially or completely hydrolyzed copolymers of vinylformamide and
vinyl acetate, vinyl alcohol, vinylpyrrolidone or acrylamide each
having molar masses of 3000-2 000 000 and also
polyethyleneimines, crosslinked polyethyleneimines or amidated
polyethyleneimines which each have molar masses from 500 to 3 000
000. The polymer content of the aqueous solution is for example
from 1 to 60%, preferably from 2 to 15% and usually from 5 to 10%
by weight.
Crosslinkers
To convert the above-described basic polymers into water-absorbing
basic polymers, they are reacted with at least one crosslinker. The
basic polymers are usually soluble or readily dispersible in water.
Crosslinking is therefore mainly carried out in an aqueous medium.
Preference is given to using aqueous solutions of basic polymers
that have been desalted, for example by ultrafiltration, or whose
neutral salt content is below 1% or below 0.5% by weight. The
crosslinkers have at least two reactive groups capable of reacting
with the amino groups of the basic polymers to form insoluble
products which are water-absorbing polymers. The amount of
crosslinker used per 1 part by weight of basic polymer is for
example in the range from 0.1 to 50 parts by weight, preferably in
the range from 1 to 5 parts by weight and especially in the range
from 1.5 to 3 parts by weight. Useful crosslinkers are described in
WO-A-00/63295 page 14 line 43 to page 21 line 5.
Useful bi- or polyfunctional crosslinkers include for example (1)
di- and polyglycidyl compounds (2) di- and polyhalogen compounds
(3) compounds having two or more isocyanate groups, which may be
blocked (4) polyaziridines (5) carbonic acid derivatives (6)
compounds having two or more activated double bonds capable of
undergoing a Michael addition (7) di- and polycarboxylic acids and
acid derivatives thereof (8) monoethylenically unsaturated
carboxylic acids, esters, amides and anhydrides (9) di- and
polyaldehydes and di- and polyketones.
Preferred crosslinkers (1) are for example the bischlorohydrin
ethers of polyalkylene glycols described in U.S. Pat. No.
4,144,123. Phosphoric acid diglycidyl ether and ethylene glycol
diglycidyl ether are also suitable.
Further crosslinkers are the products of reacting at least
trihydric alcohols with epichlorohydrin to form reaction products
having at least two chlorohydrin units, polyhydric alcohols used
being for example glycerol, ethoxylated or propoxylated glycerols,
polyglycerols having 2 to 15 glycerol units in the molecule and
also optionally ethoxylated and/or propoxylated polyglycerols.
Crosslinkers of this type are known from DE-A-2 916 356 for
example.
Useful crosslinkers (2) are .alpha.,.omega.- or vicinal
dichloroalkanes, for example 1,2-dichloroethane,
1,2-dichloropropane, 1,3-dichlorobutane and 1,6-dichlorohexane.
Furthermore, EP-A-0 025 515 discloses
.alpha.,.omega.-dichloropolyalkylene glycols having preferably
1-100, especially 1-100 ethylene oxide, units for use as
crosslinkers.
Useful crosslinkers further include crosslinkers (3) which contain
blocked isocyanate groups, for example trimethylhexamethylene
diisocyanate blocked with 2,2,6,6_tetramethylpiperidin-4-one. Such
crosslinkers are known; cf for example from DE-A-4 028 285.
Preference is further given to crosslinkers (4) which contain
aziridine units and are based on polyethers or substituted
hydrocarbons, for example 1,6-bis-N-aziridino methane, cf U.S. Pat.
No. 3,977,923. This class of crosslinkers further includes products
formed by reacting dicarboxylic esters with ethyleneimine and
containing at least two aziridino groups, and mixtures of the
crosslinkers mentioned.
Useful halogen-free crosslinkers of group (4) include reaction
products prepared by reacting ethyleneimine with dicarboxylic
esters completely esterified with monohydric alcohols of from 1 to
5 carbon atoms. Examples of suitable dicarboxylic esters are
dimethyl oxalate, diethyl oxalate, dimethyl succinate, diethyl
succinate, dimethyl adipate, diethyl adipate and dimethyl
glutarate. For instance, reacting diethyl oxalate with
ethyleneimine gives bis[.beta.-(1-aziridino)ethyl]oxalamide.
Dicarboxylic esters are reacted with ethyleneimine in a molar ratio
of 1: at least 4. The reactive groups of these crosslinkers are the
terminal aziridine groups. These crosslinkers may be characterized
for example with the aid of the formula:
##STR00001## where n is from 0 to 22.
Illustrative of crosslinkers (5) are ethylene carbonate, propylene
carbonate, urea, thiourea, guanidine, dicyandiamide or
2-oxazolidinone and its derivatives. Of this group of monomers,
preference is given to using propylene carbonate, urea and
guanidine.
Crosslinkers (6) are reaction products of polyetherdiamines,
alkylenediamines, polyalkylenepolyamines, alkylene glycols,
polyalkylene glycols or mixtures thereof with monoethylenically
unsaturated carboxylic acids, esters, amides or anhydrides of
monoethylenically unsaturated carboxylic acids, which reaction
products contain at least two ethylenically unsaturated double
bonds, carboxamide, carboxyl or ester groups as functional groups,
and also methylenebisacrylamide and divinyl sulfone.
Crosslinkers (6) are for example reaction products of
polyetherdiamines having preferably from 2 to 50 alkylene oxide
units, alkylenediamines such as ethylenediamine, propylenediamine,
1,4-diaminobutane and 1,6-diaminohexane, polyalkylenepolyamines
having molecular weights <5000 for example diethylenetriamine,
triethylenetetramine, dipropylenetriamine, tripropylenetetramine,
dihexamethylenetriamine and aminopropylethylenediamine, alkylene
glycols, polyalkylene glycols or mixtures thereof with
monoethylenically unsaturated carboxylic acids, esters of
monoethylenically unsaturated carboxylic acids, amides of
monoethylenically unsaturated carboxylic acids, and anhydrides of
monoethylenically unsaturated carboxylic acids.
These reaction products and their preparation are described in
EP-A-873 371 and are expressly mentioned for use as
crosslinkers.
Particularly preferred crosslinkers are the therein mentioned
reaction products of maleic anhydride with
.alpha.,.omega.-polyetherdiamines having a molar mass of from 400
to 5000, the reaction products of polyethyleneimines having a molar
mass of from 129 to 50 000 with maleic anhydride and also the
reaction products of ethylenediamine or triethylenetetramine with
maleic anhydride in a molar ratio of 1: at least 2.
Crosslinkers (6) are preferably compounds of the formula
##STR00002## where X, Y, Z=O, NH and Y is additionally CH.sub.2 m,
n=0-4 p, q=0-45000 which are obtainable by reacting
polyetherdiamines, ethylenediamine or polyalkylenepolyamines with
maleic anhydride.
Further halogen-free crosslinkers of group (7) are at least dibasic
saturated carboxylic acids such as dicarboxylic acids and also the
salts, diesters and diamides derived therefrom. These compounds may
be characterized for example by means of the formula
X--CO--(CH.sub.2).sub.n--CO--X where X.dbd.OH, OR.sup.1,
N(R.sup.2).sub.2 R.sup.1.dbd.C.sub.1-C.sub.22-alkyl, R.sup.1.dbd.H,
C.sub.1-C.sub.22-alkyl and n=0-22.
As well as dicarboxylic acids of the abovementioned formula it is
possible to use, for example, monoethylenically unsaturated
dicarboxylic acids such as maleic acid or itaconic acid. The esters
of the contemplated dicarboxylic acids are preferably derived from
alcohols having from 1 to 4 carbon atoms. Examples of suitable
dicarboxylic esters are dimethyl oxalate, diethyl oxalate,
diisopropyl oxalate, dimethyl succinate, diethyl succinate,
diisopropyl succinate, di-n-propyl succinate, diisobutyl succinate,
dimethyl adipate, diethyl adipate and diisopropyl adipate or
Michael addition products which contain at least two ester groups
and are formed from polyetherdiamines, polyalkylenepolyamines or
ethylenediamine and esters of acrylic acid or methacrylic acid
with, in each case, monohydric alcohols of from 1 to 4 carbon
atoms. Examples of suitable esters of ethylenically unsaturated
dicarboxylic acids are dimethyl maleate, diethyl maleate,
diisopropyl maleate, dimethyl itaconate and diisopropyl itaconate.
It is also possible to use substituted dicarboxylic acids and their
esters such as tartaric acid (D,L-form and as racemate) and also
tartaric esters such as dimethyl tartrate and diethyl tartrate.
Examples of suitable dicarboxylic anhydrides are maleic anhydride,
itaconic anhydride and succinic anhydride. Useful crosslinkers (7)
further include for example dimethyl maleate, diethyl maleate and
maleic acid. The crosslinking of amino-containing compounds with
the aforementioned crosslinkers takes place with the formation of
amide groups or, in the case of amides such as adipamide, by
transamidation. Maleic esters, monoethylenically unsaturated
dicarboxylic acids and their anhydrides can bring about
crosslinking both by formation of carboxamide groups and by
addition of NH groups of the component to be crosslinked
(polyamidoamines, for example) in the manner of a Michael
addition.
The at least dibasic saturated carboxylic acids of crosslinker
class (7) include for example tri- and tetracarboxylic acids such
as citric acid, propanetricarboxylic acid, nitrilotriacetic acid,
ethylenediaminetetraacetic acid, butanetetracarboxylic acid and
diethylenetriaminepentaacetic acid. Useful crosslinkers of group
(7) further include the salts, esters, amides and anhydrides
derived from the aforementioned carboxylic acids, e.g., dimethyl
tartrate, diethyl tartrate, dimethyl adipate and diethyl
adipate.
Useful crosslinkers of group (7) further include polycarboxylic
acids obtainable by polymerizing monoethylenically unsaturated
carboxylic acids, anhydrides, esters or amides. Examples of
suitable monoethylenically unsaturated carboxylic acids are acrylic
acid, methacrylic acid, fumaric acid, maleic acid and/or itaconic
acid. Examples of useful crosslinkers are accordingly polyacrylic
acids, copolymers of acrylic acid and methacrylic acid or
copolymers of acrylic acid and maleic acid. Illustrative comonomers
are vinyl ether, vinyl formate, vinyl acetate and vinyllactam.
Further useful crosslinkers (7) are prepared for example by
free-radical polymerization of anhydrides such as maleic anhydride
in an inert solvent such as toluene, xylene, ethylbenzene,
isopropylbenzene or solvent mixtures. Besides the homopolymers,
copolymers of maleic anhydride are suitable, for example copolymers
of acrylic acid and maleic anhydride or copolymers of maleic
anhydride and a C.sub.2- to C.sub.30-olefin.
Examples of preferred crosslinkers (7) are copolymers of maleic
anhydride and isobutene or copolymers of maleic anhydride and
diisobutene. Copolymers containing anhydride groups may optionally
be modified by reaction with C.sub.1- to C.sub.20-alcohols or
ammonia or amines and be used as crosslinkers in that form.
Examples of preferred polymeric crosslinkers (7) are copolymers of
acrylamide and acrylic esters, for example hydroxyethyl acrylate or
methyl acrylate, the molar ratio of acrylamide and acrylic ester
varying in the range from 90:10 to 10:90. Besides these copolymers,
terpolymers can be used, an example of the useful combinations
being acrylamide, methacrylamide and acrylates/methacrylates.
The molar mass M.sub.w of the homo- and copolymers useful as
crosslinkers may for example be up to 10 000, preferably from 500
to 5000. Polymers of the abovementioned type are described for
example in EP-A-0 276 464, U.S. Pat. No. 3,810,834, GB-A-1 411 063
and U.S. Pat. No. 4,818,795. The at least dibasic saturated
carboxylic acids and the polycarboxylic acids may also be used as
crosslinkers in the form of the alkali metal or ammonium salts.
Preference is given to using the sodium salts. The polycarboxylic
acids may be partially neutralized, for example to an extent of
from 10 to 50 mol %, or else completely neutralized.
Useful halogen-free crosslinkers of group (8) include for example
monoethylenically unsaturated monocarboxylic acids such as acrylic
acid, methacrylic acid and crotonic acid and the amides, esters and
anhydrides derived therefrom. The esters may be derived from
alcohols of 1-22, preferably of from 1 to 18, carbon atoms. The
amides are preferably unsubstituted, but may bear a
C.sub.1-C.sub.22-alkyl substituent.
Preferred crosslinkers (8) are acrylic acid, methyl acrylate, ethyl
acrylate, acrylamide and methacrylamide.
Useful halogen-free crosslinkers of group (9) include for example
dialdehydes or their hemiacetals or acetals as precursors, for
example glyoxal, methylglyoxal, malonaldehyde, succinaldehyde,
malealdehyde, fumaraldehyde, tartaraldehyde, adipaldehyde,
2-hydroxyadipaldehyde, furan-2,5-dipropionaldehyde,
2-formyl-2,3-dihydropyran, glutaraldehyde, pimelaldehyde and also
aromatic dialdehydes such as, for example, terephthalaldehyde,
o-phthalaldehyde, pyridine-2,6-dialdehyde or phenylglyoxal. But it
is also possible to use homo- or copolymers of acrolein or
methacrolein having molar masses of from 114 to about 10 000.
Useful comonomers include in principle all water-soluble
comonomers, for example acrylamide, vinyl acetate and acrylic acid.
Aldehyde starches are similarly useful as crosslinkers.
Useful halogen-free crosslinkers of group (9) include for example
diketones or the corresponding hemiketals or ketals as precursors,
for example .beta.-diketones such as acetylacetone or
cycloalkane-1,n-diones such as, for example, cyclopentane-1,3-dione
and cyclohexane-1,4-dione. But it is also possible to use homo- or
copolymers of methyl vinyl ketone having molar masses of from 140
to about 15 000. Useful comonomers include in principle all
water-soluble monomers, for example acrylamide, vinyl acetate and
acrylic acid.
It will be appreciated that mixtures of two or more crosslinkers
may also be used.
Preferred crosslinkers are glycidyl ethers of alkylene glycols such
as ethylene glycol, propylene glycol, 1,4-butanediol,
1,6-hexanediol and polyalkylene glycols having molar masses up to
1500 and also the completely acrylated and/or methacrylated
addition products of from 1 to 25 mol and preferably from 2 to 15
mol of ethylene oxide and 1 mol of trimethylolpropane or
pentaerythritol.
Surfactants
The polymerizable or crosslinkable aqueous mixtures include from
0.1 to 20% by weight of at least one surfactant as a further
component. The surfactants are of decisive importance for forming
and stabilizing the foam. It is possible to use anionic, cationic
or nonionic surfactants or surfactant mixtures which are compatible
with each other. It is possible to use low molecular weight or else
polymeric surfactants, and combinations of different or else
similar types of surfactants have been determined to be
advantageous. Examples of nonionic surfactants are addition
products of alkylene oxides, especially ethylene oxide, propylene
oxide and/or butylene oxide, with alcohols, amines, phenols,
naphthols or carboxylic acids. The surfactants used are
advantageously addition products of ethylene oxide and/or propylene
oxide with alcohols containing at least 10 carbon atoms, the
addition products containing from 3 to 200 mol of ethylene oxide
and/or propylene oxide per mole of alcohol. The alkylene oxide
units are present in the addition products in the form of blocks or
in random distribution. Examples of nonionic surfactants are the
addition products of 7 mol of ethylene oxide with 1 mol of tallow
fat alcohol, reaction products of 9 mol of ethylene oxide with 1
mol of tallow fat alcohol and addition products of 80 mol of
ethylene oxide with 1 mol of tallow fat alcohol. Further
commercially available nonionic surfactants comprise reaction
products of oxo process alcohols or Ziegler alcohols with from 5 to
12 mol of ethylene oxide per mole of alcohol, especially with 7 mol
of ethylene oxide. Further commercially available nonionic
surfactants are obtained by ethoxylation of castor oil. The amount
of ethylene oxide added per mole of castor oil is for example in
the range from 12 to 80 mol. Further commercially available
products are for example the reaction products of 18 mol of
ethylene oxide with 1 mol of tallow fat alcohol, the addition
products of 10 mol of ethylene oxide with 1 mol of a
C.sub.13/Cl.sub.5 oxo process alcohol or the reaction products of
from 7 to 8 mol of ethylene oxide with 1 mol of a C.sub.13/Cl.sub.5
oxo process alcohol. Useful nonionic surfactants further include
phenol alkoxylates such as for example p-tert-butylphenol which has
been reacted with 9 mol of ethylene oxide or methyl ethers of
reaction products of 1 mol of a C.sub.12-C.sub.18 alcohol and 7.5
mol of ethylene oxide.
The nonionic surfactants described above, for example by
esterification with sulfuric acid, can be converted into the
corresponding acid sulfuric esters. The acid sulfuric esters are
used in the form of their alkali metal or ammonium salts as anionic
surfactants. Useful anionic surfactants include for example alkali
metal or ammonium salts of acid sulfuric esters of addition
products of ethylene oxide and/or propylene oxide with fatty
alcohols, alkali metal or ammonium salts of alkylbenzenesulfonic
acid or of alkylphenol ether sulfates. Products of the kind
mentioned are commercially available. For example, the sodium salt
of an acid sulfuric ester of a C.sub.13/C.sub.15 oxo process
alcohol reacted with 106 mol of ethylene oxide, the triethanolamine
salt of dodecylbenzenesulfonic acid, the sodium salt of alkylphenol
ether sulfates and the sodium salt of the acid sulfuric ester of a
reaction product of 106 mol of ethylene oxide with 1 mol of tallow
fat alcohol are commercially available anionic surfactants. Useful
anionic surfactants further include acid sulfuric esters of
C.sub.13/C.sub.15 oxo process alcohols, paraffinsulfonic acids such
as C.sub.15-alkylsulfonate, alkyl-substituted benzenesulfonic acids
and alkyl-substituted naphthalenesulfonic acids such as
dodecylbenzenesulfonic acid and di-n-butylnaphthalenesulfonic acid
and also fatty alcohol phosphates such as C.sub.15/C.sub.18 fatty
alcohol phosphate. The polymerizable aqueous mixture can include
combinations of a nonionic surfactant and an anionic surfactant or
combinations of nonionic surfactants or combinations of anionic
surfactants. Even cationic surfactants are suitable. Examples
thereof are the dimethyl sulfate quaternized reaction products of
6.5 mol of ethylene oxide with 1 mol of oleylamine,
distearyldimethyl-ammonium chloride, lauryltrimethylammonium
chloride, cetylpyridinium bromide and dimethyl sulfate quaternized
triethanolamine stearate, which is preferably used as a cationic
surfactant.
The surfactant content of the aqueous mixture is preferably in the
range from 0.5 to 10% by weight. In most cases, the aqueous
mixtures have a surfactant content from 1.5 to 8% by weight.
Solubilizers
The crosslinkable aqueous mixtures may optionally include at least
one solubilizer as a further component. Solubilizers are
water-miscible organic solvents, for example dimethyl sulfoxide,
dimethylformamide, N-methylpyrrolidone, monohydric alcohols,
glycols, polyethylene glycols or monoethers derived therefrom,
subject to the proviso that the monoethers do not contain any
double bonds in the molecule. Useful ethers include methylglycol,
butylglycol, butyldiglycol, methyldiglycol, butyltriglycol,
3-ethoxy-1-propanol and glycerol monomethyl ether.
The aqueous mixtures include from 0 to 50% by weight of at least
one solubilizer. When solubilizers are used, they are preferably
included in the aqueous mixture in an amount from 1 to 25% by
weight.
Thickeners, Foam Stabilizers, Fillers, Fibers, Cell Nucleators
The crosslinkable aqueous mixture may optionally include
thickeners, foam stabilizers, fillers, fibers and/or cell
nucleators. Thickeners are used for example to optimize foam
structure and to improve foam stability. As a result, the foam will
shrink only minimally during the polymerization. Useful thickeners
include all natural and synthetic polymers known for this purpose
that substantially increase the viscosity of an aqueous system and
do not react with the amino groups of the basic polymers. The
synthetic and natural polymers in question can be swellable or
soluble in water. An exhaustive overview of thickeners may be found
for example in the publications by R. Y. Lochhead and W. R. Fron,
Cosmetics & Toiletries, 108, 95-135 (May 1993) and M. T.
Clarke, "Rheological Additives" in D. Laba (ed.) "Rheological
Properties of Cosmetics and Toiletries", Cosmetic Science and
Technology Series, Vol. 13, Marcel Dekker Inc., New York 1993.
Water-swellable or water-soluble synthetic polymers useful as
thickeners include for example high molecular weight polyethylene
glycols or copolymers of ethylene glycol and propylene glycol and
also high molecular weight polysaccharides such as starch, guar
flour, locust bean flour or derivatives of natural substances such
as carboxymethylcellulose, hydroxyethylcellulose,
hydroxymethylcellulose, hydroxypropylcellulose and mixed cellulose
ethers. A further group of thickeners are water-insoluble products,
such as finely divided silica, zeolites, bentonite, cellulose
powders and other finely divided powders of crosslinked polymers.
The aqueous mixtures may include the thickeners in amounts up to
30% by weight. When such thickeners are used at all, they are
included in the aqueous mixture in amounts of 0.1%, preferably 0.5%
up to 20% by weight.
To optimize foam structure, the aqueous reaction mixture may be
admixed, if applicable, with hydrocarbons having at least 5 carbon
atoms in the molecule. Useful hydrocarbons include for example
pentane, cyclopentane, hexane, cyclohexane, heptane, octane,
isooctane, decane and dodecane. The contemplated aliphatic
hydrocarbons can be straight-chain, branched or cyclic and have a
boiling temperature which is above the temperature of the aqueous
mixture during foaming. The aliphatic hydrocarbons extend the pot
life of the foamed aqueous reaction mixture which has not yet
polymerized. This facilitates the handling of the foams which have
not yet polymerized and increases process consistency. The
hydrocarbons act for example as cell nucleators and also stabilize
the foam which has already formed. In addition, they can effect a
further foaming of the mixture in the course of the polymerization
of the monomer foam. They can then also have the function of a
blowing agent. Instead of hydrocarbons or a mixture therewith, it
is also possible to use optionally chorinated or fluorinated
hydrocarbons as a cell nucleator and/or foam stabilizer, for
example dichloromethane, trichloromethane, 1,2-dichloroethane,
trichlorofluoromethane or 1,1,2-trichlorotrifluoroethane. When
hydrocarbons are used, they are used for example in amounts from
0.1 to 20% by weight and preferably from 0.1 to 10% by weight,
based on the polymerizable aqueous mixture.
To modify the properties of the foams, the crosslinkable aqueous
mixture may have added to it one or more fillers, for example
chalk, talc, clay, titanium dioxide, magnesium oxide, aluminum
oxide, precipitated silicas in hydrophilic or hydrophobic forms,
dolomite and/or calcium sulfate. The particle size of the fillers
is for example in the range from 10 to 1000 .mu.m and preferably in
the range from 50 to 850 .mu.m. Fillers can be included in the
crosslinkable aqueous mixture in amounts up to 30% by weight.
The properties of the foams can optionally also be modified by
means of fibers. The fibers in question can be natural or synthetic
fibers or fiber blends, for example fibers composed of cellulose,
wool, polyethylene, polypropylene, polyesters or polyamides. When
fibers are used, they may be present in the aqueous mixture in an
amount of for example up to 200% by weight and preferably up to 25%
by weight. Fillers and fibers can optionally also be added to the
ready-foamed mixture. The use of fibers leads to an enhancement of
the strength properties, such as wet strength, of the
ready-produced foam.
Water-absorbing Acidic Polymers
Useful water-absorbing acidic polymers, hereinafter also referred
to as acidic superabsorbents, include all hydrogels described for
example in WO-A-00/63295 page 2 line 27 to page 9 line 16. The
materials in question are essentially lightly crosslinked polymers
of acidic monomers that possess a high water uptake ability when in
at least partially neutralized form. Examples of such crosslinked
polymers, which are each lightly crosslinked, are crosslinked
polyacrylic acids, crosslinked hydrolyzed graft polymers of
acrylonitrile on starch, crosslinked graft polymers of acrylic acid
on starch, hydrolyzed crosslinked copolymers of vinyl acetate and
acrylic esters, crosslinked polyacrylamides, hydrolyzed crosslinked
polyacrylamides, crosslinked copolymers of ethylene and maleic
anhydride, crosslinked copolymers of isobutylene and maleic
anhydride, crosslinked polyvinylsulfonic acids, crosslinked
polyvinylphosphonic acids and crosslinked sulfonated polystyrene.
The acidic superabsorbents mentioned can be added to the
crosslinkable aqueous mixture either alone or in mixture with each
other. The acidic superabsorbents used are preferably particulate
polymers of neutralized polyacrylic acids which are lightly
crosslinked. The acid groups of the acidic superabsorbents are
preferably neutralized with aqueous sodium hydroxide solution, with
sodium bicarbonate or with sodium carbonate. The neutralization can
also be effected, however, with aqueous potassium hydroxide
solution, ammonia, amines or alkanolamines such as ethanolamine,
diethanolamine or triethanolamine.
The water-absorbing acidic polymers are added in particulate form
to the crosslinkable mixture or preferably to a ready-foamed
crosslinkable mixture. The particles can be used in solid form or
in foamed form. The weight average particle diameter is for example
in the range from 10 to 2000 .mu.m, preferably in the range from
100 to 850 .mu.m and usually in the range from 150 to 450 .mu.m.
Superabsorbents having the appropriate particle sizes can be
prepared for example by comminution, for example by grinding, of
coarsely granular, solid superabsorbents or of foamed
superabsorbents. The density of the foamed acidic superabsorbents
is for example in the range from 0.01 to 0.9 g/cm.sup.3 and
preferably in the range from 0.05 to 0.7 g/cm.sup.3. The surface of
the particulate superabsorbents can have been postcrosslinked, if
desired. It is preferable to use acidic superabsorbents whose
surface has not been postcrosslinked.
Acidic superabsorbents are known from the above-cited references,
cf in particular WO-A-00/63295 page 6 line 36 to page 7 line 44.
Surface postcrosslinking is effected, for example, by reacting
particles of lightly crosslinked polyacrylic acids with compounds
having at least two carboxyl-reactive groups. The compounds in
question are typical crosslinkers which were indicated above under
(b). Compounds which are of particular interest for use as
crosslinkers include for example polyhydric alcohols such as
propylene glycol, 1,4-butanediol or 1,6-hexanediol and glycidyl
ethers of ethylene glycol and polyethylene glycols having molar
masses from 200 to 1500 and preferably from 300 to 400 and
completely acrylated or methacrylated reaction products of
trimethylolpropane, of reaction products formed from
trimethylolpropane and ethylene oxide in a molar ratio from 1:1 to
1:25 and preferably from 1:3 to 1:15 and also of reaction products
of pentaerythritol with ethylene oxide in a molar ratio of 1:30 and
preferably a molar ratio from 1:4 to 1:20. The postcrosslinking of
the surface of the anionic superabsorbent particles is carried out
for example at up to 220.degree. C., for example preferably in the
range from 120 to 190.degree. C.
The water-absorbing acidic polymers used are superabsorbents in the
form of particles having the above-indicated particle sizes. When
water-absorbing acidic polymers are incorporated into the
crosslinkable aqueous mixture, the polymer mixture will include for
example from 10 to 90% and preferably from 30 to 70% by weight of a
water-absorbing acidic polymer. The mixture of foamed basic
hydrogel and the optionally foamed acidic hydrogel will usually
include from 40 to 60% by weight of the acidic superabsorbent.
To prepare foams which have a high absorptive ability even for
saline aqueous solutions, the basic and acidic superabsorbents are
preferably used in unneutralized form. The degree of neutralization
of the acidic water-absorbing polymers is for example from 0 to
100, preferably from 0 to 75 and usually from 0 to 50 mol %. The
water-absorbing basic polymers have a higher uptake capacity for
saline aqueous solutions and especially acidic aqueous solutions
when in the form of the free bases than in acid-neutralized form.
When basic polymers are used as sole water-absorbing polymers, the
degree of neutralization is for example from 0 to 100 and
preferably from 0 to 60 mol % %.
Superabsorbent Fiber and Fruit Fiber
According to the invention, the foam contains superabsorbent fiber
which is preferably added to the aqueous polymerizable solution
before foaming or to the foam. Superabsorbent fiber is known from
the prior art references EP-B-0 264 208, EP-B-0 272 072, EP-B-0 436
514 and U.S. Pat. No. 4,813,945. The superabsorbent fiber is
preferably fiber composed of a hydrolyzed and subsequently
crosslinked copolymer of isobutene and maleic anhydride. Instead of
isobutene, the copolymers may contain polymerized units derived
from other 1-olefins such as ethylene, propylene, diisobutylene or
styrene. The olefins mentioned and styrene are readily
copolymerizable with maleic anhydride. The copolymers are
hydrolyzed in an aqueous medium, neutralized with aqueous sodium or
potassium hydroxide solution, for example to 20-80 mol %, mixed
with crosslinkers capable of reacting with the carboxyl groups of
the copolymers (eg polyhydric alcohols, polyfunctional amines or
amino alcohols) and, after substantial removal of water, spun into
fiber. The fiber is crosslinked by heating to for example
170-240.degree. C., turning them into superabsorbents. Fiber
diameter is for example in the range from 5 to 500 .mu.m and
preferably in the range from 10 to 300 .mu.m, and fiber length is
for example in the range from 2 to 60 mm and preferably in the
range from 6 to 12 mm. The fiber is preferably added to the aqueous
polymerizable mixture, but may also be added to the foamed mixture
prior to curing by polymerization of the monomers or by
crosslinking of the basic polymers.
As well as superabsorbent fiber it is also possible to use natural
fiber. Examples of such fiber are fruit fibers such as apple fiber,
orange fiber, tomato fiber, wheat fiber and/or oat fiber. Such
fibers are commercially available. They are for example on offer
from J. Rettenmaier & Sohne GmbH & Co., Faserstoff-Werke,
D-73494 Rosenberg, under the name Vitacel.RTM.. The commercially
available natural fibers of the type mentioned are reported to have
the following fiber lengths: Apple fiber <30 .mu.m to about 1000
.mu.m Orange fiber <35 .mu.m to about 1000 .mu.m Tomato fiber
<200 .mu.m to about 2000 .mu.m Wheat fiber 30 .mu.m to 300 .mu.m
Oat fiber 35 .mu.m to 300 .mu.m.
The superabsorbent fiber and the fruit fiber are used for example
in amounts from 0.05 to 10% by weight and preferably from 0.1 to 5%
by weight, based on the polymerizable mixture. The superabsorbent
synthetic fibers have for example a Free Swell Capacity of at least
30 g/g and preferably at least 40 g/g.
Producing the Foam
The above-described crosslinkable aqueous mixtures, which contain
the monomer or the basic polymer, crosslinkers, superabsorbent
fiber and surfactant as mandatory components and also optionally at
least one further component, are initially foamed. For example, an
inert gas can be dissolved in the crosslinkable aqueous mixture at
a pressure of for example 2-400 bar and the mixture subsequently
decompressed to atmospheric. Decompression from a nozzle produces a
flowable foam. The crosslinkable aqueous mixture can also be foamed
by another method, namely by dispersing fine bubbles of an inert
gas in the crosslinkable aqueous mixture. The foaming of the
crosslinkable aqueous mixture on a laboratory scale can be effected
for example by foaming the aqueous mixture in a kitchen processor
equipped with a whisk. Foaming is preferably carried out in an
inert gas atmosphere, for example in nitrogen or noble gases under
atmospheric or superatmospheric pressure, for example up to 25 bar,
followed by decompression. The consistency of the foams, the size
of the gas bubbles and the distribution of the gas bubbles in the
foam can be varied within wide limits, for example through the
choice of surfactants, solubilizers, foam stabilizers, cell
nucleators, thickeners and fillers. As a result, the density, the
open-cell content of the foam and the wall thickness of the foam
are readily adjustable to specific values. The aqueous mixture is
preferably foamed at temperatures which are below the boiling point
of the constituents of the aqueous mixture, for example in the
range from room temperature to 100.degree. C. and preferably in the
range from 20 to 50.degree. C. However, the aqueous mixture can
also be foamed at temperatures above the boiling point of the
component having the lowest boiling point by foaming the mixture in
a pressuretightly sealed container. The foams obtained are
crosslinkable mixtures which are flowable and stable for a
prolonged period. The density of the foamed crosslinkable mixture
is for example in the range from 0.01 to 0.9 g/cm.sup.3 at
20.degree. C.
Crosslinking the Foamed Mixture
The second step of the process comprises polymerization of the
monomers or crosslinking the basic polymers to form a
water-absorbing basic polymer. The polymerization utilizes for
example crosslinkers containing two or more ethylenically
unsaturated double bonds. The polymerization is conducted in the
presence of customary radical-forming initiators. This gives
crosslinked polymers which are superabsorbant.
The originally water-soluble polymer is rendered water-insoluble by
crosslinking. A hydrogel of a basic polymer is obtained. The
crosslinkable foamed mixtures are for example transferred into
suitable molds and heated therein, so that the monomers polymerize
and the crosslinkers react with the basic polymer. The foamed
material can be applied for example in the desired thickness to a
temporary carrier material which advantageously has been provided
with an antistick coating. The foam can be knifecoated onto a
support for example. Another possibility is to fill the aqueous
foam mixture into molds which have likewise been antistick
coated.
Since the foamed aqueous mixture has a long pot life, this mixture
is also suitable for producing composite materials. For example, it
can be applied to a permanent carrier material, for example
polymeric films (films of polyethylene, polypropylene or polyamide
for example) or metal such as aluminum foils. The foamed aqueous
mixture can also be applied to nonwovens, fluff, tissues, wovens,
natural or synthetic fibers or other foams. To prepare composite
materials, it may be preferable to apply the foam in the shape of
defined structures or in different layer thickness to a carrier
material. However, it is also possible to apply the foam to fluff
layers or nonwovens and to impregnate these materials in such a way
that the fluff becomes an integral part of the foam after
crosslinking. The foamed aqueous mixture obtainable in the first
process step can also be molded into large blocks before
crosslinking. After crosslinking, the blocks can be cut or sawed
into smaller articles. It is also possible to prepare sandwichlike
structures by applying a foamed aqueous mixture to a support,
covering the foam layer with a film, foil, nonwoven, tissue, woven,
fiber or other foam and crosslinking the sandwichlike structure by
heating. However, it is also possible, before or after
crosslinking, to apply at least one further layer composed of a
foamed crosslinkable layer and if desired cover it with a further
film, foil, nonwoven, tissue, woven, fiber or other materials. The
composite is then subjected to crosslinking in the second process
step. However, it is also possible to prepare sandwichlike
structures having further foam layers of the same density or
different densities.
Inventive foam layers having a layer thickness of up to about 1
millimeter are produced for example by heating one side or in
particular by irradiating one side of the foamed polymerizable or
crosslinkable aqueous mixture. When thicker layers of a foam are to
be produced, for example foams having thicknesses of two or more
centimeters, it is particularly advantageous to heat the
crosslinkable foamed material by means of microwaves, since
relatively uniform heating can be obtained in this way. In this
case, the crosslinking is effected for example at from 20 to
180.degree. C., preferably in the range from 20 to 100.degree. C.
and especially in the range from 65 to 80.degree. C. When thicker
foam layers are to be crosslinked, the foamed mixture is heat
treated on both surfaces, for example using contact heating or by
irradiation. The density of the basic hydrogel foams is essentially
equal to the density of the crosslinkable aqueous mixture. Foams of
water-absorbing basic polymers are accordingly obtained in a
density of for example from 0.01 to 0.9 g/cm.sup.3 and preferably
from 0.1 to 0.7 g/cm.sup.3. The basic polymer foams are open
celled. The open-cell content is for example at least 80% and
preferably above 90%. Particular preference is given to foams
having an open-cell content of 100%. The open-cell content of the
foam is determined using scanning electron microscopy for
example.
Preference is given to foam which is obtainable when the
polymerizable aqueous mixture comprises at least 50% aqueous sodium
or potassium hydroxide solution neutralized acrylic acid, a
crosslinker containing at least two ethylenically unsaturated
double bonds, an initiator, superabsorbent fiber composed of
hydrolyzed and subsequently crosslinked copolymer of isobutene and
maleic anhydride, and at least one surfactant. Further examples of
superabsorbent foam are obtainable when a polymerizable aqueous
mixture is foamed which comprises at least one basic polymer
selected from the group consisting of polymers containing
vinylamine units, polymers containing vinylguanidine units,
polymers containing dialkylaminoalkyl(meth)acrylamide units,
polyethyleneimine, ethyleneimine-grafted polyamidoamines and
polydiallyldimethylammonium chlorides.
Foams having a particularly high water uptake capacity and an
improved uptake ability for electrolyte-containing aqueous
solutions are obtainable by crosslinking foamed aqueous mixtures of
basic polymers which, based on the polymer mixture, include from 10
to 90% by weight of a finely divided water-absorbing acidic
polymer. The acidic hydrogel can be present in the foams of the
invention as a solid particulate polymer or as a foamed particulate
polymer having particle sizes of for example 10-2000 .mu.m.
After the crosslinking of the foamed mixture or during the
crosslinking, the hydrogel foam is dried. This removes water and
other volatile constituents from the crosslinked hydrogel foam.
Preferably, the hydrogel foam is dried after it has been
crosslinked. Examples of suitable drying processes are thermal
convection drying, for example tray, chamber, duct, flat sheet,
disk, rotary drum, free fall tower, foraminous belt, flow,
fluidized bed, moving bed, paddle and ball bed drying, thermal
contact drying such as hotplate, drum, belt, foraminous cylinder,
screw, tumble and contact disk drying, radiative drying such as
infrared drying, dielectric drying such as microwave drying and
freeze drying. To avoid unwelcome decomposition and crosslinking
reactions, it may be advantageous to dry under reduced pressure,
under a protective gas atmosphere and/or under benign thermal
conditions where the product temperature does not exceed
120.degree. C., preferably 100.degree. C. Particularly suitable
drying processes are (vacuum) belt drying and paddle drying.
After drying, the hydrogel foam will usually no longer contain any
water. However, the water content of the foamed material can be
adjusted to any desired value by moistening the foam with liquid
water or water vapor. The water content of the gel foam is usually
in the range from 1 to 60% by weight and preferably in the range
from 2 to 10% by weight. The water content can be used to adjust
the flexibility of the hydrogel foam. Completely dried hydrogel
foams are rigid and brittle, whereas foamed materials having a
water content of for example 5-20% by weight are flexible. The
foamed hydrogels can either be used directly in the form of sheets
or granules or cut into individual plates or sheets from thicker
blocks.
However, the hydrogel foams described above can additionally be
modified to the effect that the surface of the foamed materials is
postcrosslinked. This is a way of improving the gel stability of
the articles formed from the foamed hydrogels. To perform surface
postcrosslinking, the surface of the articles formed from the
foamed hydrogels is treated with at least one crosslinking agent
and the thus treated articles are heated to a temperature at which
the crosslinkers will react with the hydrogels. Suitable
crosslinkers are described above. These compounds can likewise be
used for postcrosslinking the surface of the hydrogel foams.
Crosslinkers which are preferably used are the hereinabove
mentioned glycidyl ethers and esters of acrylic acid and/or
methacrylic acid with the reaction products of 1 mol of
trimethylolpropane and from 6 to 15 mol of ethylene oxide or
polyhydric alcohols which are used for example to postcrosslink
carboxyl-containing superabsorbent foams.
The crosslinkers for the surface postcrosslinking are preferably
applied to the foam surface in the form of an aqueous solution. The
aqueous solution can include water-miscible organic solvents, for
example alcohols such as methanol, ethanol and/or i-propanol or
ketones such as acetone. The amount of crosslinker applied to the
surface of the hydrogel foams is for example in the range from 0.1
to 5% by weight and preferably in the range from 1 to 2% by weight.
The surface postcrosslinking of the hydrogel foams is effected by
heating the hydrogel foams which have been treated with at least
one crosslinker to a temperature which is for example in the range
from 60 to 120.degree. C. and preferably in the range from 70 to
100.degree. C. After surface crosslinking, the water content of the
foamed surface-postcrosslinked hydrogel can likewise be adjusted to
values from 1 to 60% by weight.
The optionally surface-postcrosslinked hydrogel foams of the
invention can be used for all the purposes for which for example
the water-absorbing hydrogel foams which are known from EP-B-0 858
478 and which are based on acid group containing polymers such as
crosslinked polyacrylates are used. The hydrogel foams of the
invention are useful for example in hygiene articles to absorb body
fluids, in dressing material to cover wounds, as a sealing
material, as a packaging material, as a soil improver, as a soil
substitute, to dewater sludges, to absorb aqueous acidic wastes, to
thicken waterborne paints or coatings in the course of disposing of
residual quantities thereof, to dewater water-containing oils or
hydrocarbons or as a material for filters in ventilation
systems.
Of particular importance is the use of the hydrogel foams of the
invention in hygiene articles, such as baby diapers, sanitary
napkins and incontinence articles, and in dressing material. In
hygiene articles for example they perform more than one function,
namely acquire, distribute and/or store body fluids. The surface of
the hydrogel foams can optionally be modified by treatment with
surfactants or polymers containing uncrosslinked vinylamine units.
This provides an improvement in the acquisition of fluids.
Layers of the hydrogel foams according to the invention can be for
example disposed in a thickness from 1 to 5 mm in one of the
abovementioned hygiene articles as an absorbent core between a
liquid-pervious topsheet and a liquid-impervious layer composed of
a film of for example polyethylene or polypropylene. The
liquid-pervious layer of the hygiene article is in direct contact
with the skin of the user. This material is customarily composed of
a nonwoven of natural fibers such as cellulose fibers or fluff. If
desired, a tissue layer will be disposed above and/or below the
absorbent core. Between the bottom layer of the hygiene article and
the absorbent core, there may optionally be a storage layer
composed of a conventional particulate anionic superabsorbent. When
the foamed basic hydrogels are used as an absorbent core in
diapers, the open-cell structure of the foamed basic hydrogel will
ensure that the body fluid, which is normally applied in individual
amounts all at once, is speedily removed. This gives the user a
pleasant sense of the surface dryness of the diaper.
Methods of Determination
Density
Any suitable gravimetric method can be used for determining the
density of the multicomponent foam system. What is determined is
the mass of solid multicomponent foam system per unit volume of
foam structure. A method for density determination of the
multicomponent foam system is described in ASTM Method No. D
3574-86, Test A. This method was originally developed for the
density determination of urethane foams, but can also be used for
this purpose. By this method, the dry mass and volume of a
preconditioned sample is determined at 22+/-2.degree. C. Volume
determination of larger sample dimensions are carried out under
atmospheric pressure.
Free Swell Capacity (FSC)
This method is used to determine the free swellability of the
multicomponent foam system in a teabag. To determine FSC,
0.2000.+-.0.0050 g of dried foam is introduced into a teabag
60.times.85 mm in size, which is subsequently sealed shut. The
teabag is placed in an excess of test solution (at least 0.83 l of
sodium chloride solution/1 g of polymer) for 30 minutes. The teabag
is subsequently allowed to drip for 10 minutes by being hung up by
one corner. The amount of liquid is determined by weighing back the
teabag.
The test solution used was 0.9% by weight NaCl solution.
Centrifuge Retention Capacity (CRC)
This method is used to determine the free swellability of the
multicomponent foam system in a teabag. To determine CRC,
0.2000.+-.0.0050 g of dried multicomponent foam is introduced into
a teabag 60.times.85 mm in size, which is subsequently sealed shut.
The teabag is placed in an excess of 0.9% by weight sodium chloride
solution (at least 0.83 l of sodium chloride solution/1 g of
polymer) for 30 minutes. The teabag is then centrifuged at 250 G
for 3 minutes. The amount of liquid is determined by weighing back
the centrifuged teabag.
The test solution used was 0.9% by weight NaCl solution
Free Swell Rate (FSR)
To determine the free swell rate, 0.50 g (W.sub.H) of the
multicomponent foam system is placed on the base of a plastic dish
having a round bottom of about 6 cm. The plastic dish is about 2.5
cm deep and has a square opening of about 7.5 cm.times.7.5 cm. A
funnel is then used to add 10 g (W.sub.U) of a 0.9% NaCl solution
into the center of the plastic dish. As soon as the liquid has
contact with the multicomponent foam system, time measurement is
started and not stopped until the multicomponent foam system has
completely taken up the entire liquid, ie until pooled liquid is
absent. This time is noted as t.sub.A. The free swell rate then
computes from FSR=W.sub.U/(W.sub.H.times.t.sub.A). K value
The K value was determined after H. Fikentscher, Cellulose-Chemie,
Volume 13, 52-63 and 71-74 (1932) in 5% by weight aqueous solution
at pH 7, 25.degree. C. and a polymer concentration of 0.5% by
weight.
Wet Failure Value (WFV) of Superabsorbent Foam
The Wet Failure Value is the force needed to destroy a test
specimen of a fully swollen superabsorbent foam under controlled
conditions in the hereinbelow described apparatus. The
superabsorbent foam is swollen in synthetic urine or in 0.9% by
weight aqueous sodium chloride solution until it ceases to take up
liquid.
The Wet Failure Value is measured in a commercially available
texture analyzer (TA-XT2) from Stable Micro Systems, Surrey, UK.
The measuring instrument is diagrammed in FIG. 1. A measuring arm
(1) has attached to it a sphere (2) of stainless steel 1 inch (2.54
cm) in diameter that can be brought to bear on a sample of the
swollen superabsorbent foam (3) held between two metal plates. Both
the metal plates have a hole in the middle that has a diameter
r1=5.1 cm and a diameter r2=3.5 cm, cf FIG. 2. As is revealed by
FIG. 3, the side of the plate with the r1 diameter has a rounded
shape which corresponds to a quarter segment of a circle having a
diameter of 0.8 cm. Only this side of each plate comes into contact
with the superabsorbent foam to be analyzed. The rounded shape--cf
FIG. 3--is important in order that the foam being analyzed is not
damaged by sharp-edged corners in the course of testing. The place
surfaces which come into contact with the foam are roughened in
order that the foam may be held in place during testing.
The plates each are 0.8 cm thick and have edge lengths a=10 cm and
b=9 cm. The foam sample is located between the two plates as
indicated above. The instrument is set to a load of 5000 g. To
determine the wet failure value, the sphere (2) connected to the
measuring arm (1) is then lowered at a speed of 0.5 mm/s and the
force needed to destroy the foam sample is measured. The maximum
distance which the sphere (2) travels in the course of measurement
is 30 mm. The sphere pushes through the foam situated between the
two plates. The requisite force per unit area is determined and
reported as WFV in g/mm.sup.2.
Three samples are prepared of each foam and measured as described
above. It is important here that the foam samples to be analyzed do
not contain holes or comparatively large air inclusions, since they
would falsify the measurements.
Determination of Thickness of Swollen Foam
The thickness of the swollen foam was determined by means of a
Digimatic thickness gauge from Mitutoyo. The thickness of the foam
was measured as soon as it was fully swollen.
Cross Sectional Area (CSA)
The area of the cross section is determined on the fully swollen
foam by considering only that area which is obtained from the
diameter (r2=35 mm) and the thickness of the swollen foam in the
equilibrium state (Te) by the following formular:
CSA[mm.sup.2]=35.times.Te Wet Failure Point
is the maximum force (F) [g] which is indicated in the texture
analyzer by the peak maximum and which is needed to destroy the
fully swollen foam sample in the texture analyzer of FIG. 1.
Wet Failure Value (WFV)
is obtained from the maximum force (F) needed to destroy the
swollen foam sample and the Cross Sectional Area of the fully
swollen foam as per WFV[g/mm.sup.2]=maximum force/CSA
Superabsorbent Fiber
The Fiberdri.RTM. superabsorbent fiber from Camelot Technologies
Limited, Canada, that is used in the examples is based on
crosslinked hydrolyzed copolymers of isobutene and maleic anhydride
after partial neutralization with aqueous sodium hydroxide
solution.
The OASIS.RTM. superabsorbent fiber from Technical Absorbents
Limited, UK, also used in the examples are based on crosslinked
copolymers of sodium acrylate, hydroxypropyl acrylate and methyl
acrylate.
Unless suggested otherwise by the context, the percentages in the
examples are by weight.
Preparation of an Acidic Particulate Water-absorbing Polymer (SAP
1)
270 g of acrylic acid were weighed into a beaker. 1.155 g of
methylenebisacrylamide (MBA) crosslinker were then added, the
monomers were stirred until everything had dissolved. 810 g of
distilled water were weighed into a separate vessel and added to
the monomer mixture. The solution was stirred to complete the
mixture. The aqueous monomer solution was subsequently stored in a
freezer cabinet for cooling for about 1 hour.
A 10% sodium persulfate solution was prepared with distilled water
and added to a cooled polymerization tank. 0.157 g of
2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur.RTM. 1173, Ciba,
photoinitiator) and 2.736 g of the 10% sodium persulfate solution
were added as initiator system. A final mixing step provided the
homogenous system which was left until it had attained a
temperature of 10.degree. C., at which the polymerization reaction
was then carried out within 12 minutes by irradiating with a UV
dose of 20 mWcm.sup.-2. This provided a gellike addition polymer,
which was comminuted and fully dried at 125.degree. C. The dried
addition polymer obtained was ground and the fraction having an
average particle size of 150 .mu.m-450 .mu.m was sieved off.
EXAMPLES
Inventive Example 1
The following components were mixed in a beaker by means of a
magnetic stirrer:
TABLE-US-00001 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 0.5% by
weight on monomers (2.4 g) of superabsorbent fiber (Fiberdri P8/00
1231, ex Camelot Technologies Limited, Canada). The solution
obtained was transferred into a pressure vessel and saturated
therein with carbon dioxide at 12 bar for 25 min. 26.67 g of a 3%
aqueous solution of 2,2'-azobis(2-amidinopropane) dihydrochloride
were added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00002 Solids content of reaction mixture: 81.74% Degree of
neutralization: 60 mol % Monomer foam density: 0.24 gcm.sup.-3
Polymer foam density: 0.20 gcm.sup.-3 Foam structure: homogeneous,
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 2
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00003 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 1.0% by
weight on monomers (4.8 g) of superabsorbent fiber (Fiberdri P8/00
1231, ex Camelot Technologies Limited, Canada). The solution
obtained was transferred into a pressure vessel and saturated
therein with carbon dioxide at 12 bar for 25 min. 26.67 g of a 3%
aqueous solution of 2,2'-azobis(2-amidinopropane) dihydrochloride
were added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00004 Solids content of reaction mixture: 82.13% Degree of
neutralization: 60 mol % Monomer foam density: 0.28 gcm.sup.-3
Polymer foam density: 0.22 gcm.sup.-3 Foam structure: homogeneous,
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 3
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00005 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 3% by
weight on monomers (14.40 g) of superabsorbent fiber (Fiberdri
P8/00 1231, ex Camelot Technologies Limited, Canada). The solution
obtained was transferred into a pressure vessel and saturated
therein with carbon dioxide at 12 bar for 25 min. 26.67 g of a 3%
aqueous solution of 2,2'-azobis(2-amidinopropane) dihydrochloride
were added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiations (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00006 Solids content of reaction mixture: 81.99% Degree of
neutralization: 60 mol % Monomer foam density: 0.26 gcm.sup.-3
Polymer foam density: 0.21 gcm.sup.-3 Foam structure: homogeneous
fully open cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 4
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00007 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 0.1% by
weight on monomers (0.48 g) of superabsorbent fiber (Fiberdri P8/00
1231, ex Camelot Technologies Limited, Canada). The solution
obtained was transferred into a pressure vessel and saturated
therein with carbon dioxide at 12 bar for 25 min. 26.67 g of a 3%
aqueous solution of 2,2'-azobis(2-amidinopropane) dihydrochloride
were added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00008 Solids content of reaction mixture: 81.43% Degree of
neutralization: 60 mol % Monomer foam density: 0.21 gcm.sup.-3
Polymer foam density: 0.19 gcm.sup.-3 Foam structure: homogeneous
fully open cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Invention Example 5
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00009 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of
polyethylene glycol diacrylate of a polyethylene glycol of molar
mass 400 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 1.0% by
weight on monomers (4.8 g) of superabsorbent fiber (Fiberdri P8/00
1231, ex Camelot Technologies Limited, Canada). The solution
obtained was transferred into a pressure vessel and saturated
therein with carbon dioxide at 12 bar for 25 min. 26.67 g of a 3%
aqueous solution of 2,2'-azobis(2-amidinopropane) dihydrochloride
were added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00010 Solids content of reaction mixture: 82.13% Degree of
neutralization: 60 mol % Monomer foam density: 0.23 gcm.sup.-3
Polymer foam density: 0.20 gcm.sup.-3 Foam structure: homogeneous
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 6
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00011 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 1% by
weight on monomers (0.48 g) of superabsorbent fiber (OASIS.RTM. ex
Technical Absorbents Limited, UK). The solution obtained was
transferred into a pressure vessel and saturated therein with
carbon dioxide at 12 bar for 25 min. 26.67 g of a 3% aqueous
solution of 2,2'-azobis(2-amidinopropane) dihydrochloride were
added under pressure and homogeneously mixed in by raising the
pressure. This was followed by passing carbon dioxide through the
reaction mixture for a further 5 min. The saturated reaction
mixture was expressed at 12 bar through a die 1 mm in diameter to
form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00012 Solids content of reaction mixture: 82.13% Degree of
neutralization: 60 mol % Monomer foam density: 0.33 gcm.sup.-3
Polymer foam density: 0.29 gcm.sup.-3 Foam structure: homogeneous
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 7
To 300 g of a 10% ultrafiltered aqueous solution of polyvinylamine
(PVAm) having a K value of 90 were added 15 g of a 5% aqueous
solution of a commercially available surfactant (addition product
of 80 mol of ethylene oxide with 1 mol of C16/C18 alcohol mixture)
and 15 g of a 5% aqueous solution of ethylene glycol diglycidyl
ether crosslinker.
The crosslinkable mixture was then foamed in the shearing zone of
an Ultraturrax stirrer for 1 minute. To samples of the
crosslinkable aqueous mixture were then added 1% by weight (0.3 g),
based on PVAm, of a superabsorbent fiber (Fiberdri P8/00 1231, ex
Camelot Technologies Limited, Canada). The mixture was then stirred
for 1 minute. This gave a homogeneous mixture. The foamed
crosslinkable mixtures thus prepared were each poured onto a Teflon
support rimmed with aluminum. The mold containing the foamed
crosslinkable mixture was stored at 70.degree. C. in a drying
cabinet overnight. The hydrogel foam obtained was subsequently
adjusted to a water content of 5%.
TABLE-US-00013 Solids content of reaction mixture: 10% Degree of
neutralization: 0 mol % Polymer foam density: 0.18 gcm.sup.-3 Foam
structure: homogeneous, fully open-cell
Further properties of the open-cell foam are reported in Tables 1
and 2.
Inventive Example 8
To 300 g of a 10% ultrafiltered aqueous solution of polyvinylamine
having a K value of 90 were added 15 g of a 5% aqueous solution of
a commercially available surfactant (addition product of 80 mol of
ethylene oxide with 1 mol of C16/C.sub.1-8 alcohol mixture) and 15
g of a 5% aqueous solution of ethylene glycol diglycidyl ether
crosslinker.
The crosslinkable mixture was then foamed in the shearing zone of
an Ultraturrax stirrer for 1 minute. To samples of the
crosslinkable aqueous mixture were added first 45 g of SAP 1 and
then 1% by weight (0.3 g), based on PVAm, of a superabsorbent fiber
(Fiberdri P8/00 1231, ex Camelot Technologies Limited, Canada). The
mixture was then stirred for 1 minute. This gave a homogeneous
mixture. The foamed crosslinkable mixtures thus prepared were each
poured onto a Teflon support rimmed with aluminum. The mold
containing the foamed crosslinkable mixture was stored at
70.degree. C. in a drying cabinet overnight. The hydrogel foam
obtained was subsequently adjusted to a water content of 5%.
TABLE-US-00014 Solids content of reaction mixture: 22.5% Polymer
foam density: 0.20 gcm.sup.-3 Foam structure: homogeneous, fully
open-cell
Further properties of the open-cell foam are reported in Tables 1
and 2.
Comparative Example 1
Comparison as per Example 1 of WO-A-00/52087
The following components were mixed in a beaker by means of a
magnetic stirrer:
TABLE-US-00015 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of
polyethylene glycol diacrylate of a polyethylene glycol of molar
mass 400 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. The solution obtained was transferred into a
pressure vessel and saturated therein with carbon dioxide at 12 bar
for 25 min. 26.67 g of a 3% aqueous solution of
2,2'-azobis(2-amidinopropane) dihydrochloride were added under
pressure and homogeneously mixed in by raising the pressure. This
was followed by passing carbon dioxide through the reaction mixture
for a further 5 min. The saturated reaction mixture was expressed
at 12 bar through a die 1 mm in diameter to form a free-flowing
fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass
plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00016 Solids content of reaction mixture: 81.04% Degree of
neutralization: 60 mol % Monomer foam density: 0.21 gcm.sup.-3
Polymer foam density: 0.20 gcm.sup.-3 Foam structure: homogeneous,
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 1
and 2.
TABLE-US-00017 TABLE 1 Example FSC [g/g] CRC [g/g] FSR [g/gsec]
Inventive 1 50.3 11.0 4.9 Inventive 2 48.2 10.9 4.6 Inventive 3
44.4 11.2 4.2 Inventive 4 50.0 10.4 5.5 Inventive 5 50.5 8.3 7.9
Inventive 6 36.0 10.8 2.9 Inventive 7 41.7 12.3 1.9 Inventive 8
38.5 19.4 0.2 Comparative 1 56.6 7.7 4.4
TABLE-US-00018 TABLE 2 Swollen foam Wet Failure thickness CSA Point
WFV Example [mm] [mm.sup.2] [g] [g/mm.sup.2] Inventive 1 5.41 189.3
47.0 0.269 Inventive 2 6.03 211.1 60.3 0.340 Inventive 3 6.48 226.8
44.2 0.234 Inventive 4 7.80 273.0 66.8 0.245 Inventive 5 9.46 331.1
50.4 0.152 Inventive 6 8.38 293.3 90.8 0.310 Inventive 7 8.70 304.5
262.3 1.315 Inventive 8 10.09 353.2 158.5 0.423 Comparative 1 12.60
441.0 41.0 0.093
Inventive Example 9
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00019 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution of an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. The solution obtained was transferred into a
pressure vessel and saturated therein with carbon dioxide at 12 bar
for 25 min. 26.67 g of a 3% aqueous solution of
2,2'-azobis(2-amidinopropane) dihydrochloride were added under
pressure and homogeneously mixed in by raising the pressure. This
was followed by passing carbon dioxide through the reaction mixture
for a further 5 min. The saturated reaction mixture was expressed
at 12 bar through a die 1 mm in diameter to form a free-flowing
fine-cell foam.
Into a mold, an A4-size glass plate having rims 1 mm high, was
placed a 0.69 mm thick nonwoven web of superabsorbent (Fiberdri
P8/00 1231, ex Camelot Technologies Limited, Canada) having a web
density of 0.0995 g/cm.sup.3 and the previously prepared monomer
foam was then applied to the web and carefully worked into the web
while keeping the open-cell foam structure intact. The mold was
then covered with a second glass plate. The foam sample was then
polymerized between the two glass plates by irradiating the glass
plates simultaneously from both sides with two UV/VIS radiators (UV
1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00020 Solids content of reaction mixture: 81.35% Degree of
neutralization: 60 mol % Monomer foam density: 0.22 gcm.sup.-3
Polymer foam density with web: 0.29 gcm.sup.-3 Foam structure:
homogeneous, fuly open-cell, no skin Foam and web: 458
g/m.sup.2
Further properties of the open-cell foam are reported in Table
3.
TABLE-US-00021 TABLE 3 Dry foam Swollen foam Wet failure thickness
thickness CSA point WFV Example [mm] [mm] [mm.sup.2] [g]
[g/mm.sup.2] Inv. 9 1.75 3.25 113.75 25.7 0.226
Inventive Example 10
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00022 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of an
ethoxylated trimethylolpropane triacrylate of molar mass 956
(ETMPTA) 21.33 g of a 15% aqueous solution in an addition product
of 80 mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 1.0% by
weight (4.8 g), based on monomers, of apple fiber (Bio-Apfelfaser
AF 400, ex J. Rettenmaier & Sohne GmbH & Co, Germany). The
solution obtained was transferred into a pressure vessel and
saturated therein with carbon dioxide at 12 bar for 25 min. 26.67 g
of a 3% aqueous solution of 2,2'-azobis(2-amidinopropane)
dihydrochloride were added under pressure and homogeneously mixed
in by raising the pressure. This was followed by passing carbon
dioxide through the reaction mixture for a further 5 min. The
saturated reaction mixture was expressed at 12 bar through a die 1
mm in diameter to form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00023 Solids content of reaction mixture: 82.13% Degree of
neutralization: 60 mol % Monomer foam density: 0.25 gcm.sup.-3
Polymer foam density: 0.27 gcm.sup.-3 Foam structure: homogeneous,
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 4
and 5.
Inventive Example 11
The following components were mixed in a beaker by means of a
magnetic stirrer.
TABLE-US-00024 348.55 g of acrylic acid (4.84 mol) 135.51 g of a
37.3% sodium acrylate solution in water (0.54 mol) 28 g of
polyethylene glycol diacrylate of polyethylene glycol of molar mass
400 21.33 g of a 15% aqueous solution of an addition product of 80
mol of ethylene oxide to 1 mol of a linear saturated
C.sub.16C.sub.18 fatty alcohol 65.70 g of water
To this solution were added with ice cooling 400.90 g (2.69 mol) of
triethanolamine such that the internal temperature did not rise
above 16.degree. C. To the aqueous mixture was then added 1.0% by
weight (4.8 g), based on monomers, of apple fiber (Bio-Apfelfaser
AF 400, ex J. Rettenmaier & Sohne GmbH & Co, Germany). The
solution obtained was transferred into a pressure vessel and
saturated therein with carbon dioxide at 12 bar for 25 min. 26.67 g
of a 3% aqueous solution of 2,2'-azobis(2-amidinopropane)
dihydrochloride were added under pressure and homogeneously mixed
in by raising the pressure. This was followed by passing carbon
dioxide through the reaction mixture for a further 5 min. The
saturated reaction mixture was expressed at 12 bar through a die 1
mm in diameter to form a free-flowing fine-cell foam.
The monomer foam obtained was applied to an A3-size glass plate
having rims 3 mm high and was covered with a second glass plate.
The foam sample was irradiated simultaneously from both sides with
two UV/VIS radiators (UV 1000 from Hohnle) for 4 minutes.
The foam layer obtained was fully dried in a vacuum drying cabinet
at 70.degree. C. and subsequently adjusted to a moisture content of
5% by spraying with water.
TABLE-US-00025 Solids content of reaction mixture: 82.13% Degree of
neutralization: 60 mol % Monomer foam density: 0.22 gcm.sup.-3
Polymer foam density: 0.17 gcm.sup.-3 Foam structure: homogeneous,
fully open-cell, no skin
Further properties of the open-cell foam are reported in Tables 4
and 5.
TABLE-US-00026 TABLE 4 Teabag test (FSC) Example [g/g] CRC [g/g]
FSR [g/gsec] Inventive 10 43.7 10.1 1.74 Inventive 11 55.2 8.1
6.68
TABLE-US-00027 TABLE 5 Swollen foam thickness CSA Wet Failure Point
WFV Example [mm] [mm.sup.2] [g] [g/mm.sup.2] Inventive 10 6.62
231.7 89.6 0.387 Inventive 11 9.31 325.8 58.8 0.180
* * * * *